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Simple Exponential Backoff Retry Class in C++
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Simple Exponential Backoff Retry Class in C++

April 23, 2021 No Comments c / c++

As a user – I want to build a simple retry library, which retries on error and has a mechanism to do an exponential backoff. For example:

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var err = SendtoNetwork.Send();
retry = new Retry(err);
retry.now();
var err = SendtoNetwork.Send();
retry = new Retry(err);
retry.now();

Lets define a payload to invoke the network call with:

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class Payload {
  // adding other parameters
  string data;
};
class Payload {
  // adding other parameters
  string data;
};

We can have a retry policy to specify the max Retries, time between retries etc.

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class RetryPolicy {
  int maxRetries;
  int timeBetweenRetries;
 
  public RetryPolicy WithMaxRetries(int m) {   
    this->maxRetries = m;
    return this;
  }
};
class RetryPolicy {
  int maxRetries;
  int timeBetweenRetries;
 
  public RetryPolicy WithMaxRetries(int m) {   
    this->maxRetries = m;
    return this;
  }
};

Let’s define a function call signature

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typedef function<void(Payload)> FUNC;
typedef function<void(Payload)> FUNC;

Then in the Retry class, we pass in the payload, the function, the retry policy:

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class Retry {
  public:
    Retry(FUNC func, Payload &payload, RetryPolicy retryPolicy): 
         func(func), maxRetries(maxRetries), payload(payload) {
      numOfTries = 0;
    }
 
    void now() {
      while (numOfTries < maxRetries) {
        try {        
          func(payload);        
          break;
        } catch (std::exception &ex) {
          if (numOfTries ++ <= retryPolicy.maxRetries) {
              sleep(1 << numOfTries);
          } else {
              throw std::run_time_exception(ex, "exceeded max retries");
          }
        }
      }
    }
 
  private:
    FUNC func;
    Payload payload;
    int numOfTries;
    int maxRetries;
}
class Retry {
  public:
    Retry(FUNC func, Payload &payload, RetryPolicy retryPolicy): 
         func(func), maxRetries(maxRetries), payload(payload) {
      numOfTries = 0;
    }
 
    void now() {
      while (numOfTries < maxRetries) {
        try {        
          func(payload);        
          break;
        } catch (std::exception &ex) {
          if (numOfTries ++ <= retryPolicy.maxRetries) {
              sleep(1 << numOfTries);
          } else {
              throw std::run_time_exception(ex, "exceeded max retries");
          }
        }
      }
    }
 
  private:
    FUNC func;
    Payload payload;
    int numOfTries;
    int maxRetries;
}

And in the execute (now) function, we call the function with payload, and if we can still retry – then, we retry otherwise we throw a runtime exception. The first time, it will wait 1 second before next retry, and then wait for 2 seconds, 4 seconds – exponential strategy.

–EOF (The Ultimate Computing & Technology Blog) —

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